This invention relates to windows and, in particular, to a window that is transparent to visible and/or infrared radiation but is opaque to electromagnetic radiation.
Sensors operating in the visible or infrared wavelength bands are widely used in civilian and military applications. Such sensors are usually rather fragile in construction and susceptible to externally induced damage. They are therefore often placed behind a protective window that is transparent to the radiation being sensed but resists damage from hostile physical and chemical environmental effects, impacts, and the like.
Such a mechanically protective window is sufficient for some applications, but in other cases, such as many military applications, the window must also protect against penetration of radio frequency energy to the sensor. Various techniques are known for attenuating incident radio frequency energy while allowing the transmission of the visible or infrared radiation of interest. These techniques operate by a variety of reflection and absorption mechanisms. For example, it is known to place a metallic grid pattern formed of narrow, electrically conductive metallic stripes onto the surface of the window, which grid pattern reflects the incident radio frequency energy away from the window while passing most of the visible or infrared radiation.
While operable, such metallic grid patterns still permit the passage of some of the incident radio frequency energy through the window. The inventor has recognized a need for an improved approach wherein an even smaller amount of the incident radio frequency energy passes through the window, while still permitting the passage of the visible or infrared radiation of interest. The present invention fulfills this need, and further provides related advantages.